The invention relates to a fuel injector for use in supplying fuel, under pressure, to a combustion space of a compression ignition internal combustion engine. In particular, the invention relates to a fuel injector of the outwardly opening type.
Known fuel injectors of the outwardly opening type include a valve needle, slidable within a bore and engageable with a seating to control the supply of fuel from the bore. The valve needle is moved outwardly of the bore to move the needle away from its seating under the control of a piezoelectric actuator. The distance through which the valve needle is moved is typically controlled by controlling the energization level, and hence the axial length, of a piezoelectric stack. Such an actuation technique is thought to be undesirable as piezoelectric stacks of dimensions suitable for use in such applications are relatively expensive and can be difficult to control.
It is an object of the present invention to provide a fuel injector of the outwardly opening type in which the distance moved by the valve needle can be controlled by alternative means.
According to the present invention, there is provided a fuel injector of the outwardly opening type comprising a nozzle body provided with a first bore, a valve needle slidable within the bore and engageable with a seating to control the supply of fuel from the bore, first and second control chambers for receiving fuel under pressure and control valve means for controlling the fuel pressure within the first and second control chambers, the valve needle being moveable in response to a change in fuel pressure in at least one of the first and second control chambers.
The fuel injector of the present invention therefore uses hydraulic means to control movement of the valve needle. The control valve means can therefore be operated conveniently by means of an electromagnetic actuator arrangement. The cost of the fuel injector is therefore reduced compared to fuel injectors in which valve needle movement is controlled by means of a piezoelectric actuator. Furthermore, it is easier to control movement of the valve needle with greater accuracy.
Alternatively, the control valve member may be operated by means of a piezoelectric actuator.
In one embodiment of the invention, the control valve means may include a single control valve member having first and second valve seatings, whereby movement of the control valve member away from the first valve seating only causes movement of the valve needle into a first fuel injecting position and movement of the control valve member away from both the first and second valve seatings causes movement of the valve needle into a second fuel injecting position.
The valve needle may include first and second fuel outlet passages axially spaced on the valve needle such that, when the valve needle is in the first fuel injecting position, fuel is only discharged through the first outlet passage and, when the valve needle is in the second fuel injecting position, fuel is also discharged through the second outlet passage. In this way, the rate of fuel injection into the engine can be carefully controlled.
Conveniently, the fuel injector includes a thrust member, moveable in response to a change in fuel pressure in at least one of the first and second control chambers, the thrust member acting on the valve needle to control valve needle movement.
The valve needle may be provided with further outlet passages and the control valve means may be arranged to control movement of the valve needle between first, second and further fuel injecting positions.
In an alternative embodiment, the control valve means may include two control valve members for controlling the fuel pressure within the first and second control chambers independently.